This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-289147 filed on Sep. 21, 2001 and Japanese Patent Application No. 2002-058653 filed on Mar. 5, 2002.
1. Field of the Invention
The present invention relates to a magnetic member for an electromagnetic driving device and a manufacturing method thereof.
2. Description of Related Art
In one previously proposed electromagnetic driving device, a movable core is attracted toward a stationary core when a corresponding coil wound around the stationary core is energized to generate a magnetic flux in a magnetic circuit. Such an electromagnetic driving device is widely used, for example, in a flow control valve, which opens and closes a flow passage by a valve member that reciprocates integrally with the movable core.
When the coil is energized, a density of the magnetic flux, which flows through the magnetic circuit formed by the stationary core and the movable core, increases. However, for example, as shown in FIG. 12, when the density of the magnetic flux increases, an eddy current 310 flows through the stationary core 300. The eddy currents 310 flow in such a manner that the eddy currents 310 reduce the density of the magnetic flux in the stationary core 300. Thus, a magnetic force of the stationary core 300, which attracts the movable core is reduced.
In order to restrain such a reduction in the magnetic force caused by the eddy currents, i.e., to reduce the eddy current loss, it has been proposed to form slits in the stationary core and/or the movable core to interrupt the region, through which the eddy current flows. However, the slits reduce a surface area of the magnetic passage, resulting in a reduction in the magnetic force.
Apart from the magnetic member for the electromagnetic driving device, Japanese Unexamined Patent publication No. 2001-143217 discloses a magnetic head. The magnetic head includes a metal magnetic film. The metal magnetic film is made of metal magnetic layers and insulation layers, which are alternately stacked through various thin film forming techniques, such as an sputtering process and a vacuum deposition process, in order to reduce eddy current loss in the metal magnetic film. The insulation layers are provided to reduce the eddy currents generated in the metal magnetic film, thereby reducing the eddy current loss.
However, the thin film forming techniques, such as the sputtering process and the vacuum deposition process, can only provide a relatively thin metal magnetic film. As a result, it is difficult to form a magnetic member that requires a relatively large magnetic passage surface area, such as the stationary core and the movable core used in the electromagnetic driving device of the flow control valve, by the thin film forming techniques, such as the sputtering process and the vacuum deposition process.
Thus, it is an objective of the present invention to provide a magnetic member for an electromagnetic driving device for generating a magnetic attracting force of a desired magnitude without substantially increasing its size. It is another objective of the present invention to provide a manufacturing method of such a magnetic member.
To achieve the objectives of the present invention, there is provided a magnetic member, which forms at least part of a magnetic circuit of an electromagnetic driving device. The magnetic member includes a plurality of magnetic portions and a plurality of bonding thin layers, each of which is interposed between corresponding adjacent ones of the magnetic portions to join the adjacent ones of the magnetic portions. A volume resistivity of each bonding thin layer is greater than that of iron. The adjacent ones of the magnetic portions are joined together by diffusion bonding in such a manner that the corresponding bonding thin layer is interposed between the adjacent ones of the magnetic portions.
To achieve the objectives of the present invention, there is provided a method for manufacturing a magnetic member for an electromagnetic driving device. In the method, a plurality of magnetic material bodies, each of which has a magnetic portion, is provided. A bonding thin layer, which has a volume resistivity greater than that of iron, is formed on one or more surfaces of each of at least one of the magnetic material bodies. A structure, which has a predetermined shape, is constructed from the magnetic material bodies in such a manner that the bonding thin layer of each of the at least one of the magnetic material bodies is interposed between each of the at least one of the magnetic material bodies and one or more corresponding adjacent magnetic material bodies. Then, each of the at least one of the magnetic material bodies is joined to the one or more corresponding adjacent magnetic material bodies in such a manner that the bonding thin layer of each of the at least one of the magnetic material bodies is interposed between each of the at least one of the magnetic material bodies and the one or more corresponding adjacent magnetic material bodies. The joining of each of the at least one of the magnetic material bodies to the one or more corresponding adjacent magnetic material bodies is accomplished at least by placing the structure in an enclosed space, evacuating the enclosed space, and inducing diffusion between each of the at least one of the magnetic material bodies and the one or more corresponding adjacent magnetic material bodies.
To achieve the objectives of the present invention, there is further provided a method for manufacturing a magnetic member for an electromagnetic driving device. In the method, a structure, which has a predetermined shape, is constructed from a plurality of magnetic material bodies. Then, adjacent ones of the magnetic material bodies are joined together in such a manner that a corresponding oxidized thin layer is interposed between the adjacent ones of the magnetic material bodies. Each oxidized thin layer has a volume resistivity greater than that of iron. The joining of the adjacent ones of the magnetic material bodies is accomplished at least by placing the structure in an enclosed space, supplying oxygen gas into the enclosed space, evacuating the enclosed space, and heating the structure to induce diffusion between the adjacent ones of the magnetic material bodies.
To achieve the objectives of the present invention, there is also provided a method for manufacturing a magnetic member for an electromagnetic driving device. In the method, a structure, which has a predetermined shape, is constructed from a plurality of magnetic material bodies. Then, adjacent ones of the magnetic material bodies are joined together in such a manner that a corresponding nitrided thin layer is interposed between the adjacent ones of the magnetic material bodies. Here, each nitrided thin layer has a volume resistivity greater than that of iron. The joining of the adjacent ones of the magnetic material bodies is accomplished at least by placing the structure in an enclosed space, supplying nitrogen gas into the enclosed space, evacuating the enclosed space, and inducing diffusion between the adjacent ones of the magnetic material bodies.